I have not commented in this thread, partly out of a sense of humility that there are people who are more f**ked up than I am. I am impressed. Really.
I have been prone to minor depression all my life, and it has not helped my writing one bit. In fact it has killed my creativity stone dead, for years at a time.
Depression, and the related but different condition of stress, are complex subjects. Depression can take different forms: from quiet desperation to wild mood swings; it can have obvious triggers or be inexplicable; and like most mental health issues it exists on a continuum, from the "not-quite-normal" to the barking. Human beings cultural evolution has outstripped our physiological adaptation and it is not entirely surprising that just about everyone finds it difficult to cope at times, or that they respond in different ways.
Our brain configuration and chemistry determine how we respond to life, but a the same time our experience of life shapes our brain chemistry and configuration. There is a feedback loop, which is why it is important to seek treatment - so that a response to trauma does not become a personality trait. There is no virtue in just soldering on.
My GP tells me he is always happy when someone comes to him complaining of depression, because it is one of the few conditions he can actually do something about. The drugs are not just placebos - they can work, if you get the right medication and the right dose. After a couple of months on Prozac I was sceptical about the benefits, then the doc doubled the dose. And it was a case of, "wow! is this how normal people feel all of the time?"
I have a member staff who is going through a difficult and protracted marital break-up; she has not been sleeping, and has been very emotional and erratic. She had tried anti-depressants but had not got on with them. I persuaded her to go back to her GP and try again. She is now as happy as Larry - and able to deal with her c**t of a husband and sort her life out.